The present invention relates to a X-ray radiographing method and a radiographing apparatus capable of being applicable to medical service and non-destructive test, in particular, to a X-ray radiographing method and a radiographing apparatus capable of depicting a boundary of a radiographed object with high contrast.
When an object is irradiated with X-ray emitted from a X-ray source, difference in transmission amount of X-ray transmitting the object is caused by difference in atomic weight of materials constituting the radiographed object. Accordingly, an X-ray image can be formed by detecting the two dimensional distribution of the transmission amount of X-ray.
Incidentally, since X-ray is an electromagnetic wave, X-ray has a nature of a wave. Accordingly, when X-ray transmits an object, diffraction or refraction is caused by deviation in phase and the diffraction or the refraction can be detected as an image. Conventionally, a X-ray image formation by utilizing the above nature has not been conducted. However, recently, a method of radiographing a X-ray image of an object with high contrast by utilizing the above nature has been suggested. The X-ray image obtained by this method is called a phase contrast X-ray image. In this image, since the contrast at a boundary region of the object may be enhanced, the detected ability of a X-ray image can be increased. Therefore, the method is desired to be applied to medical service using X-ray and non-destructive test for industry.
Several propositions regarding the method and the apparatus for obtaining the phase contrast X-ray image have been made. However, these techniques are insufficient in the point of actual use at a working spot where an image is obtained.
For example, in an official publication of TOKKAIHEI 10-248833, a phase contrast X-ray radiographing apparatus according to a interference method employing a Mach Zehnder type interferometer by using a synchrotron radiation X-ray has been suggested. Further, in “Medical Applications of Synchrotron Radiation” (M. Ando and C. Uyamam eds., Springer-Verlag Tokyo, 1998), a lot of technical reports to apply the phase contrast X-ray image by using the synchrotron radiation X-ray to medical service are described.
These methods are conducted by using the synchrotron radiation X-ray generating apparatus. This apparatus can obtain a strong monochromic X-ray in the form of a spatial coherent parallel light. The form that X-ray is “spatial coherent” or “lateral spatial coherent” provides the characteristics that the X-ray has coherence as wave.
Here, the synchrotron radiation X-ray generating apparatus is set up recently as “SPring-8” in Akou-districts Hyogo-prefecture and also in the physical construction science research institute in a higher energy accelerator research organization. However, these apparatus are too huge constructions to be utilized by private medical facilities and needs a huge amount of construction cost. Therefore, these apparatus have hardly been utilized by a private facility for medical purpose or other inspections.
Further, Wilkins reported a method of obtaining a phase contrast X-ray image from a fish or a small animal by using a micro focus X-ray source and the radiographing method for the X-ray image is described in the patent publication WO 96/31098. In this publication, Wilkins describes a X-ray image radiographing apparatus and a radiographing method by using the apparatus in which a X-ray source having a size of focal spot deemed as a spot light source such as a size of focal spot not larger than 20 μm is used in order to obtain X-ray having a high lateral spatial coherence and the distance between an object to be radiographed and a X-ray detector is set more than 0.3 m.
In the above science magazine, there is reported an experiment result in which a micro focus X-ray source having the size of focal spot of 20 μm used and a fish or a small animal is used as an object to be radiographed. In the method reported by Wilkins, since the size of focal spot of the X-ray tube is too small, X-ray is obtained by only a small radiation amount. Accordingly, it is reported that in the X-ray image radiography for fish, the radiographing time of about 2 hours was needed to obtain a X-ray image on a silver salt photographic film. From the above report, it may be difficult to widely apply the above method to a clinical site to radiograph a human body or to an inspection for a substance. On the other hand, if a size of focal spot is made larger, the penumbra is caused by the size of focal spot. Therefore, there may happen that the sharpness of an image is lowered or an unsharp image is caused.